1. Field of the Invention
The present invention relates to a cathode ray tube, and, in particular, to a color cathode ray tube having a color selection mechanism or the like.
2. Description of the Related Art
In manufacture of a cathode ray tube, welding is performed to connect a metal member to a metal member.
For example, as shown in FIG. 1, a color selection mechanism 5 which is installed to the inside of a color selection mechanism is assembled in such a way that a metal frame 6 and another metal member, for example, a color selection electrode 61 are welded together.
The color selection electrode 61 is such that a plurality of apertures are provided in a thin metal plate.
Also, a shield member 62 made of a thin metal plate is attached to the frame 6 by welding.
The shield member 62 is attached in order to protect the orbit of an electron beam from deviating due to the influences of the earth""s magnetic field or the like as well as to reduce changes in color purity of an image displayed on a cathode ray tube.
Generally, at a time of welding the metal member, fine metal powder sputters to the peripheral portion thereof from the welding spot due to a thermal shock of the welding and adheres to the surface of the metal member.
When the fine power of this kind is in a state capable of moving freely, however, there is a case wherein the fine powder moves inside of the cathode ray tube due to vibration or the like.
For example, it is conceivable that the fine powder moves and adheres to the vicinity of an electron gun.
Since a high voltage is applied to the cathode ray tube when it is in operation, a strong electric field is generated in the vicinity of the electron gun.
When the strong electric field acts on the fine powder, there is a case wherein an instantaneous discharge occurs.
Since the discharge of this kind triggers such phenomena as an occurrence of noise to the image displayed on the cathode ray tube, or the like, it is intrinsically not needed in terms of the operation of the cathode ray tube.
Therefore, in the manufacturing process of the cathode ray tube, it is desirable that the fine powder which has adhered to the metal member be removed and not left inside of the cathode ray tube not to be capable of moving freely.
To this end, there are carried out steps to remove the metal-adhered fine powder by an air blow, suction or degaussing and the like.
However, when welding is performed to the portions to be welded by superimposing two metal members, fine powder adheres to a gap between the metal members.
It is also conceivable that the fine powder which has adhered to the gap moves about inside of the cathode ray tube due to the vibrations or the like.
However, because of the structure it is extremely difficult to completely remove the fine powder adhering to the gap.
Meanwhile, the amount of generated fine powder is influenced by the relations between two metal members, for example, such as differences in thickness, materials and the like of the two metal members.
Generally, the larger is the difference in thickness, the stronger becomes a propensity in which the amount of the generated fine powder becomes large.
In many cases, metal parts used for the cathode ray tube are manufactured by welding metal members different in thickness.
And the amount of the generated fine powder is influenced by welding conditions.
Particularly, two metal members which are in a relationship wherein the amount of the generated fine powder is larger, for example, in the case of welding members having a large difference in thickness are much influenced by the welding conditions in terms of the amount of the generated fine powder.
Generally, when the welding conditions are adjusted so as to reduce the generation of the fine powder, there exists a relationship wherein strength at a welded portion becomes weak.
On the contrary, when the welding conditions are adjusted so as to increase the strength of the welded portion, there exists a relationship wherein the generated amount of the fine power increases.
Consequently, when the welding strength is to be increased, the generated amount of the fine powder increases and when the fine powder is prevented from generating it becomes difficult to sufficiently secure the welding strength.
When electric spot welding is used, the welding conditions are adjusted by the value of a welding current and the value of a voltage of welding electrodes.
However, even when these values are varied, it has been difficult to find optimum conditions, for example, conditions under which the fine powder is hardly generated and high strength is sufficiently secured.
On the other hand, when connection is performed using connection members such as screws or bolts in place of connection by welding, the generation of the fine powder can be restrained.
However, the number of parts increases and operations in the manufacturing steps become cumbersome.
As a result, the manufacturing cost increases.
Also, strength of the connection by screws and bolts is in many cases weaker than by welding.
In order to solve the problem described above, the present invention provides a cathode ray tube which can prevent the fine powder generated by welding from later appearing due to vibration or the like and which can be easily manufactured at a low cost.
A cathode ray tube according to the present invention is such that a metal part within the cathode ray tube comprises a first member and a second member.
The first and second members may be different in thickness as well as material.
And said first member and second member have welding points at portions where they are superimposed.
Further, the present invention is characterized in that a hermetic space is formed so as to surround the welding points between the first member and second member.
The present invention is used in the case where, for example, said first member is the frame of a color selection mechanism and said second member is an internal magnetic shield.
The hermetic space may have such a constitution wherein said second member is attached to the first member having a recessed portion at a welding portion so as to cover the recessed portion.
Also, the hermetic space may have such a constitution wherein the second member with a recessed portion being formed around a welding spot is attached to the first member.
According to said constitution, the fine powder generated at the time of welding is contained in the hermetic space.
As a result, it is possible to prevent the fine powder from moving inside the cathode ray tube due to vibration or the like.
Moreover, welding which put emphasis on welding strength becomes possible.